1. Field of the Invention
The present invention relates to a variable traffic safety sign for roads and highways, and more particularly, to a variable traffic safety sign for variably displaying wet roadbed and freezing conditions of a road or bridge section in the form of a figure or characters using a thermochromic paint and a paint for a humidity indicator card (“HIC”) so as to inform road users of the possibility of a surface of the road or bridge section being wet or frozen.
2. Discussion of Related Art
Generally, wet surfaces and freezing are main causes of traffic accidents caused due to vehicle slipping occurring on surfaces of roads. In particular, since a bottom surface of a bridge section is exposed to the air, a surface of the bridge section has a high possibility of being frozen, compared to a surface of a road having terrestrial heat.
FIG. 1 is a diagram showing a side view a conventional bridge section being exposed to the air.
As shown in FIG. 1, if the bottom surface of the bridge section is exposed to the air, pavement of the bridge has a high possibility of being frozen when the temperature drops below the freezing point, resulting in a further increased risk for accidents. In particular, drivers may inadvertently mistake a wet road surface for shade at night when it is difficult to visually identify whether a surface of the road is wet or frozen due to the drivers' poor visibility, or when a thin freezing film referred to as ‘black ice’ occurs on the road, which results in a very high risk for accidents.
The road management agency or authority has installed traffic safety sign boards at bridge entry to inform drivers of such a possibility of surfaces of the bridge entry being wet or frozen, as shown in FIGS. 2A to 2D.
FIGS. 2A to 2D are images showing examples of traffic safety sign boards installed at bridge entry according to the prior art. Here, the traffic safety sign boards for displaying wet roadbed and freezing conditions are installed at the bridge entry.
However, such traffic safety sign boards may not easily attract drivers since the traffic safety sign boards are always installed at fixed places, and also always require constant attention regardless of current roadbed conditions, and thus are not really helpful for safe driving.
Meanwhile, since the road is wet with moisture due to rain, snow, dew, and the like, an increase in humidity in the air or on the road surface increases a possibility of a surface of the road being wet. Also, when the temperature of the air or road surface drops below the freezing point, moisture present on or around the road, for example rain, snow, dew, water vapor and the like, is changed into ice crystals. Accordingly, as the temperature of the road or the air drops below the freezing point under a high humidity condition, a surface of the road is highly likely to be frozen.
To solve the above problems, as prior-art documents, Japanese Patent Laid-open Publication No. 1996-22259 titled “Road Sign” discloses a road sign capable of easily and quickly displaying dangerous road conditions caused by the air, and Japanese Patent Laid-open Publication No. 2003-193440 titled “Roadbed Marker” also discloses a roadbed marker whose color is changed according to conditions such as a temperature, where the roadbed marker may be simply displayed to call drivers' attention to the surrounding conditions such as road surface freezing, etc.
Also, as another prior-art document, Korean Unexamined Patent Application Publication No. 2015-0081585 discloses a “Paint Composition for Indicating Whether the Ground is Frozen.” Referring to FIG. 3A and FIG. 3B, the paint composition will be described.
FIG. 3A and FIG. 3B are a diagram schematically showing a principle of displaying whether or not the ground is frozen using a paint composition according to the prior art.
Referring to FIG. 3A, the paint composition for displaying whether or not the ground is frozen according to the prior art may display whether or not the ground is frozen as the paint composition changes in color by sensing the moisture and temperature of the ground. In this case, the paint composition includes 10 to 30 parts by weight of a temperature-sensing material which changes in color at a temperature of 32° F. or less, and a 10 to 30 parts by weight of a moisture-sensing material which changes in color by sensing moisture, based on 100 parts by weight of the paint.
When the paint composition for displaying whether or not the ground is frozen according to the prior art is applied to traffic lanes of highways, the paint composition may sense a temperature of 32° F. or less, and a change in moisture on a surface of a road caused due to rain or snow, as shown in FIG. 3B. In this way, the paint composition may display a change in color of the traffic lanes, thereby visually displaying that the ground is frozen.
However, the paint composition for displaying whether or not the ground is frozen according to the prior art may display whether the ground is merely frozen because it is formed to include both the temperature-sensing material and the moisture-sensing material. Therefore, the paint composition has a problem in that it is difficult to exactly display the roadbed conditions of the road.
Meanwhile, FIG. 4A and FIG. 4B are diagrams for explaining a humidity indicator card according to the prior art. Here, FIG. 4A shows a humidity indicator card having regions for detecting a relative humidity of 10%, 20%, 30%, 40%, 50% and 60%, and FIG. 4B shows compositions of a paint for a humidity indicator card, which are formed by mixing copper (II) sulfate pentahydrate, sodium bromide, water and a dye solution to detect various relative humidity levels.
As shown in FIGS. 4A and 4B, a humidity indicator card may be used to determine a relative humidity, and compositions of the paint for a humidity indicator card may be varied to detect various relative humidity levels.
According to the prior art, an additional external power source should be used to inform road users of roadbed conditions such as a freezing or wet roadbed conditions of the road or bridge section, or the above-mentioned paint composition for displaying whether the ground is frozen has a problem in that it is difficult to exactly display the roadbed conditions of the road since the paint composition displays only whether or not the ground is frozen.